Polymer Synthesis Methods and Processes

Polymer Synthesis Methods and Processes 2.2.2.1 Polymer Synthesis... 

Polymer Synthesis Methods and Processes 5.2.2.1 Postsulfonation Method... 

UHMWPE is not just a simple sequence of methylenes -(CH2)-, but it also contains small but measurable concentrations of vinyl double bonds, tertiary carbons, and methyl groups. These short and long chain branches, as well as the residues of the catalyst, are incorporated in the less ordered amorphous phase, not in the crystalline lamellae. The amounts of structural irregularities, as well as the degree of crystallinity, depend on the polymer synthesis method and on the subsequent processing conditions of the resin. 

In order to understand how synthetic polymers are prepared, the methods and processes of polymerisation are presented in this chapter and Chapter 4. It can be seen that some properties of polymers, especially surface properties, depend on the synthesis. The classical techniques are introduced first, but the more specific techniques needed to synthesise special polymers are emphasised. 

There are other important polymerization processes such as those of the suspension or emulsion type. Examples of these two types are given in Figs. 4.55 and 4.56. For an excellent description of the synthesis and kinetics of polymerization methods and processes the reader is referred to more detailed texts focusing on polymer science, eg. Painter and Coleman, (1994) and Billmeyer, (1984). 

An elegant synthesis method which is specific to sulfone polymers containing phenyl—phenyl linkages (such as PPSF) is the nickel-catalysed coupling of aryl dihahdes. The scheme for this synthesis involves a two-step process. First, an aromatic dihaUde intermediate is formed which carries the backbone features of the desired polymer. This aromatic dihahde intermediate is then self-coupled in the presence of sero-valent nickel, triphenylphosphine, and excess sine to form the biphenyl- or terphenyl-containing polymer. AppHcation of this two-step scheme to PPSF can be depicted as follows ... 

Radical polymerization is the most useful method for a large-scale preparation of various kinds of vinyl polymers. More than 70 % of vinyl polymers (i. e. more than 50 % of all plastics) are produced by the radical polymerization process industrially, because this method has a large number of advantages arising from the characteristics of intermediate free-radicals for vinyl polymer synthesis beyond ionic and coordination polymerizations, e.g., high polymerization and copolymerization reactivities of many varieties of vinyl monomers, especially of the monomers with polar and unprotected functional groups, a simple procedure for polymerizations, excellent reproducibility of the polymerization reaction due to tolerance to impurities, facile prediction of the polymerization reactions from the accumulated data of the elementary reaction mechanisms and of the monomer structure-reactivity relationships, utilization of water as a reaction medium, and so on. 

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